text: * Reduced cellular defense mechanisms
  ** Children younger than 4 months exposed to various environmental agents
  ** Pregnant women are considered vulnerable to exposure of high levels of nitrates in drinking water
  ** Cytochrome b5 reductase deficiency
  ** G6PD deficiency
  ** Hemoglobin M disease
  ** Pyruvate kinase deficiency
  * Various pharmaceutical compounds
  ** Local anesthetic agents, especially prilocaine and benzocaine.
  ** Amyl nitrite, chloroquine, dapsone, nitrates, nitrites, nitroglycerin, nitroprusside, phenacetin, phenazopyridine, primaquine, quinones and sulfonamides
  * Environmental agents
  ** Aromatic amines (e.g. p-nitroaniline, [http://www.gtfch.org/cms/images/stories/media/tk/tk73_2/Bakdash.pdf patient case])
  ** Arsine
  ** Chlorobenzene
  ** Chromates
  ** Nitrates/nitrites
  ** Umbellulone
  * Inherited disorders
  ** Some family members of the Fugate family in Kentucky, due to a recessive gene, had blue skin from an excess of methemoglobin.
  * In cats
  **Ingestion of paracetamol (i.e. acetaminophen, tylenol)